1. Field of the Invention
This invention relates to therapeutic agents and peptides, radiotherapeutic agents and peptides, and radiodiagnostic agents and peptides. Specifically, the invention relates to cyclic peptide derivatives and analogues of somatostatin, and embodiments of such peptides labeled with radioisotopes of iodine.
2. Description of the Prior Art
Somatostatin is a tetradecapeptide that is endogenously produced by the hypothalamus and pancreas in humans and other mammals. The peptide has the formula: ##STR1## (Single letter abbreviations for amino acids can be found in G. Zubay, Biochemistry (2d ed.), 1988, (MacMillan Publishing: New York), p.33). This peptide exerts a wide variety of biological effects in vivo. It is known to act physiologically on the central nervous system, the hypothalamus, the pancreas, and the gastrointestinal tract.
Somatostatin inhibits the release of insulin and glucagon from the pancreas, inhibits growth hormone release from the hypothalamus, and reduces gastric secretions. Thus, somatostatin has clinical and therapeutic applications for the alleviation of a number of ailments and diseases, both in humans and other animals. Native somatostatin is of limited utility, however, due to its short half-life in vivo, where it is rapidly degraded by peptidases. For this reason, somatostatin analogues having improved in vivo stability have been developed in the prior art.
Freidinger, U.S. Pat. No. 4,235,886 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Coy and Murphy, U.S. Pat. No. 4,485,101 disclose synthetic dodecapeptide somatostatin analogues.
Freidinger, U.S. Pat. No. 4,611,054 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Nutt, U.S. Pat. No. 4,612,366 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Coy et al., U.S. Pat. No. 4,853,371 disclose synthetic octapeptide somatostatin analogues.
Coy and Murphy, U.S. Pat. No. 4,871,717 disclose synthetic heptapeptide somatostatin analogues.
Coy et al., U.S. Pat. No. 4,904,642 disclose synthetic octapeptide somatostatin analogues.
Taylor et al., U.S. Pat. No. 5,073,541 disclose a method of treating small cell lung cancer.
Brady, European Patent Application No. 83111747.8 discloses dicyclic hexapeptide somatostatin analogues useful in the treatment of a number of human diseases.
Bauer et al., European Patent Application No. 85810617.2 disclose somatostatin derivatives useful in the treatment of a number of human diseases.
Eck and Moreau, European Patent Application No. 90302760.5 disclose therapeutic octapeptide somatostatin analogues.
Coy and Murphy, International Patent Application Serial No. PCT/US90/07074 disclose somatostatin analogues for therapeutic uses.
Schally et al., European Patent Application Serial No. EPA 911048445.2 disclose cyclic peptides for therapeutic use.
Bodgen and Moreau, International Patent Application Serial No. PCT/US92/01027 disclose compositions and method for treating proliferative skin disease.
Somatostatin exerts its effects by binding to specific receptors expressed at the cell surface of cells comprising the central nervous system, the hypothalamus, the pancreas, and the gastrointestinal tract. These high-affinity somatostatin binding sites have been found to be abundantly expressed at the cell surface of most endocrine-active tumors arising from these tissues. Expression of high-affinity binding sites for somatostatin is a marker for these tumor cells, and specific binding with somatostatin can be exploited to locate and identify tumors cells in vivo.
Methods for radiolabeling somatostatin analogues that have been modified so as to contain a tyrosine amino acid (Tyr or Y) are known in the prior art.
Albert et al., UK Patent Application 8927255.3 disclose radioimaging using somatostatin derivatives such as octreotide labeled with .sup.123 I.
Bakker et al., 1990, J. Nucl. Med. 31: 1501-1509 describe radioactive iodination of a somatostatin analog and its usefulness in detecting tumors in vivo.
Bakker et al., 1991, J. Nucl. Med. 32: 1184-1189 teach the usefulness of radiolabeled somatostatin for radioimaging in vivo.
Bomanji et al., 1992, J. Nucl. Med. 33 1121-1124 describe the use of iodinated (Tyr-3) octreotide for imaging metastatic carcinoid tumors.
The use of chelating agents for radiolabeling proteins are known in the prior art, and methods for labelling peptides with Tc-99m are disclosed in co-pending U.S. patent applications Ser. Nos. 07/902,935, now U.S. Pat. No. 5,716,596, 08/092,355, and 08/095,760, now U.S. Pat. No. 5,620,675, and PCT International Applications PCT/US93/06029, which are hereby incorporated by reference.
Many of the somatostatin receptor-binding peptides known in the prior art have been found to have poor bioavailability when tested for use as therapeutic agents, and poor biodistribution when tested for use as diagnostic agents, due to their high lipophilicity and consequently rapid uptake by the liver. Accordingly, there remains a need in the art for synthetic somatostatin receptor-binding compounds that have high in vivo stability and yet are sufficiently hydrophilic that they do not undergo rapid hepatic clearance from the synthetic circulation upon administration. The small synthetic peptides of the present invention fulfill this need in the art.